1. Field of the Invention
The present invention pertains to gas lift apparatus and more specifically to side pocket mandrels and gas lift valves for disposition therein. The purpose and function of gas lift valves generally is well known in the art and will not be described in great detail herein. Briefly, such apparatus is used to facilitate petroleum production in wells in which the formation pressure alone is not sufficient to force the oil to the surface. A typical production well includes a casing lining the well bore and a smaller string of production tubing suspended within the casing so as to define an annulus between the two conduits. In many instances, oil is recovered by causing it to flow upwardly through the inner string of production tubing. In other instances, the oil is caused to flow upwardly through the annulus between the tubing and casing. In any event, assuming that the production tubing (or annulus, depending upon the technique being used) has a column of oil therein, the pressure head of such liquid column may exceed the formation pressure so that the latter cannot force the oil upwardly through the well. Of course, if the formation pressure is exceedingly low, it may be necessary to actively pump the oil from the well. However, in some instances, there is sufficient formation pressure so that, if the density of the column of oil can be reduced, the oil can be caused to flow upwardly without such pumping.
In order to so reduce the density of a column of oil in a well, gas lift valves are frequently employed. Such a valve is typically disposed in a side pocket in a special mandrel. If the oil is being recovered through the tubing, gas is pumped into the annulus. Conversely, if the oil is being recovered from the annulus, gas is pumped into the tubing. In any event, the gas lift valve permits the gas so pumped into the well to pass through the side pocket of the mandrel, which forms a part of the production tubing string, and into the column of oil. As the gas bubbles upwardly through the column, it reduces the column's density as described hereinabove.
2. Description of the Prior Art
The conventional side pocket mandrel for receipt of a gas lift valve includes only a single inlet and a single outlet, and the corresponding valve includes the same number of general ingress or egress areas. Such pockets and valves provide adequate gas flow for gas lift operations for wells in which the maximum potential production rate is low to moderate. However, since the sizes of the inlets and outlets cannot be made too large without sacrificing proper functioning of the valve in general and proper regulation of gas flow, e.g. the emission of gas into the column of oil in the form of relatively small bubbles which may be dispersed throughout the column decreasing its density, such conventional valves may not provide sufficient volume of gas flow for relatively high capacity wells, e.g. those capable of producing on the order of 50,000 barrels per day.
Past and present solutions to the problem of providing adequate flow for gas lift operations in high capacity wells have generally required an excessive number of parts and consumption of space on the production string, and have been expensive, awkward, and generally troublesome. One such prior approach has been to run a series of side pocket mandrels, each with its respective gas lift valve, immediately above one another in the production string so that there are, for example, two or three such valves operating at roughly the same depth. Another approach has been to provide a mandrel with multiple side pockets disposed about its circumference, with a separate gas lift valve in each of these pockets. It should be apparent that each of these two prior approaches suffers from the general disadvantages described hereinabove.